Cannabis: Polishing extracts

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Some MMJ applications require greater purity and potency, so it is desirable to remove inactive ingredients like fats, lipids, and plant waxes, as well as any chlorophyll and other water solubles.

When I class chlorophyll with the water solubles, it is not in the same vein as the term is used in inorganic chemistry and is more involved.  Chlorophyll itself has a polar head and hydrophobic tail, so it is mostly non soluble in polar water, but can be removed from the plant and conveyed by water as micelle.

Water also dissolves and washes away the Chlorophyll binding proteins and exposes the Chlorophyll to the solvent used.  Chlorophyll is highly soluble in alcohol and slightly soluble in butane.

For further discussion of that subject, please see: /chlorophyll-pickup-in-extractions/

Processes that use a polar solvent and reflux or soxhlet to maximize extraction, also maximize and concentrate chlorophyll, which can be a problem for some people.  The poison is in the dosage, so even for a salubrious ingredients like chlorophyll, some people can get too much of a good thing, producing digestive tract upsets, with attendant vomiting, cramps, and diarrhea.

See:  for details.

In a nutshell, many water soluble non cannabinoid ingredients come along for the ride when a polar solvent is used and water is present. While it is easier to use a process that minimizes their extraction in the first place, if that is a moot point, because you already have an extraction with excessive non-active ingredients, here are some ways to clean them up:


After re-dissolving the extract in ethanol or hexane, it may simply be filtered to remove the material that is insoluble.  We usually use coffee filters for this purpose, or if we have a larger amount, we use a Whatman # 1 lab filter, with a vacuum assist.

If we wish to filter it further, we run it through 0.45 or 0.2 micron syringe filters, which takes out any remaining plant material, as well as any bacteria present.


When using non polar solvents like butane and hexane, some non-polar waxes, fats, and lipids are extracted as well.  An easy way to get rid of them is to simply re-dissolve the non-polar extraction in 190 proof (~95.5% azeotropic) polar ethanol and stick it in the freezer for about 48 hours at -18C/0F, for the waxes to coagulate.

The waxes will precipitate out of solution as the temperature drops and clump together so that they are easily filtered out with a standard coffee filter, or a Whatman #1 lab filter.

Here is what a winterizing filter cake looks like, while still wet.After filtering, the alcohol is evaporated or vacuumed off, to leave a pristine Absolute.

Winterizing ISO, Methanol, and Denatured alcohol extractions:

Even though Ethanol is polar itself, it can still be used to remove some of the undesirables they pick up, because it is not as aggressive a solvent as Isopropyl and Methanol.  By re-dissolving their extracts in hot ethanol and then placing that in the freezer overnight, some of the undesirables will precipitate out and may be filtered out.

Removing minor green coloration:

Because butane is non polar and considered insoluble in water, it is the longest chain alkane that is still slightly water soluble at 0.0325 vol/vol (3.25%).  That means that a liter of n-butane will actually hold as much as 32.5 ml or mgs of water (1000ml X 0.0325).

3.25% by volume is also enough water to bring along some water solubles like chlorophyll and leave an otherwise pristine extraction with a green tint, usually light and sometimes a gorgeous electric hue.

These light green hues are easily removed without the more involved and extreme measures that I will follow up with, and is as simple as putting a jar of the oil suspended in an ethanol tincture, in sunlight or a light from a high UV source, like a grow lamp.

The UV radiation in the sunlight will quickly break down the chlorophyll and the breakdown products are amber, so the green color disappears. Alas, UV radiation also destroys cannabinoids, but fortunately at a much slower rate, and three or four hours in the sun is usually enough.


Oops!  Soooo, what if the extraction is really, really messed up, or if you just want to see how purdy you can make an extract?

Sometimes bad things happens to good oil, and evil spirits need to be exorcised, or sometimes the most economical process, or indeed the only available extraction process, extracts undesirables.  Fortunately there are ways to remove undesirables, though at the expense of yield and some of the other terpenes, so there is compromise involved.

Alcohol/Hexane wash:

One way to clean up an alcohol extraction, is to reduce its volume to a manageable level given your resources, and pour it in a separatory funnel to about the one third level, followed by the same volume of n-Hexane and then of water.

We use an HPLC Reagent grade for this purpose, which we get from the local scientific supply store.Shake well and then lift the lid long enough to burp any pressure, before setting it in a stand to stratify into layers.  After it has separated, bleed off the water and emulsion layer.  They contain both the undesirables, and the alcohol as well, with the cannabinoids left with the hexane.

Add water again and repeat the wash step until you are satisfied with the clarity, before evaporating off the hexane, to yield the pristine oil.  More on hexane purging in the subsequent process description for serious scrubbing:

To put this process into perspective, I once collected all of my pipe bowl  scrapings and roaches until I had about a pint of them, and dumped that into the container of black denatured alcohol, that I had been cleaning my pipes in.

I shook the mixture well and let it soak for a day to extract the material from the roaches and scrapings, before straining it through a wire strainer and then a coffee filter.

Because I didn’t want to mess up a separatory funnel with the black foul smelling mess, I poured the solution in a 1 gallon Ziploc bag, to which I added equal amounts of water and hexane.

After shaking it well, I hung it from one corner, to let it stratify, and after it had, I clipped off the lower corner of the Ziploc bag, and by pinching it, and controlling the bleed rate, I was able to bleed off the water, alcohol, and emulsion layer, so that only the now gold hexane solution remained.

I filtered the hexane and poured that into a Pyrex pie plate, which I blew air over with a fan to evaporate off.  Attached are pictures of the amber oil that I extracted.

While the black color was gone, slight ashtray undertones could still be tasted, so further refining was necessary with activated charcoal, but we will cover that as a separate subject.

I am not suggesting this process for reclaiming ashtrays, but simply to make a point.

Hexane/Saline water wash:

Joe came up with this process, which has produced our most pristine creations.  It involves  re-dissolving the oil in a hot highly non-polar solvent such as hexane and repeatedly washing the solution with saturated salt water until it is mint quality.

Salt water washing uses a separatory funnel as above, but we start out dissolving the extraction to be cleaned directly into hot n-Hexane, and then washing the hexane solution with saturated salt water.

The magic trick is two fold.  The saline exposes any proteins hydrophobic surfaces, making them insoluble in water, so that they precipitate out, and the saturated water has no room for anything but the alcohol, which aids that process.

We start out by making four or five liters of saturated salt water in a glass (or ceramic) container, by mixing sodium chloride (table salt) in hot tap water with a hand mixer until no more will dissolve. We buy the salt cheap by the bag, using salt intended for water softener use.

We perform the salt water wash of the hexane mixture, by simply pouring the salt water and hexane into the separatory funnel together in about equal parts and shaking well and burping, before allowing the mixture to separate out into layers.

After carefully bleeding off the bottom layer of water, we continue to replace it and repeat the wash process of both the emulsion layer and the hexane solution, until the emulsion layer disappears and the hexane has bell clear clarity.

At that point we stop washing and evaporate off the hexane. While we use HPLC grade hexane, light naphtha containing only Pentane & Hexane will also work for this process.  Check the MSDS because the word light naphtha only means it boils between 30C and 100C, so it can contain Benzene..

Purging Hexane:

While n-Hexane is a delightfully non polar solvent, that enables us to do some amazing things, it has two more carbons and four more hydrogen atoms in the chain than Butane, and so due to the greater Van der Waal forces involved, is not as easy to get rid of as Butane.

The most effective way that we’ve found to remove the residual hexane, is either with multiple ethanol washes, usually around three, or thin film vacuum.

To wash with ethanol, redissolve the hexane honey oil in ethanol at a ration of about 10 to one and boil off the alcohol.  When it is almost all gone, do it again, and repeat, until there is no decernable hexane odor.

For thin film evaporation, we place about .200 inch of it in a six inch Petri dish, which we place in a vacuum chamber and evacuate down to 29.5 mm Hg and ~80F for 30 minutes.

N-Hexane boils at about 69 °C/ 156 °F and has a high vapor pressure, so it is easy to evaporate, but harder to completely purge.  Given our 30ppm taste sensory threshold and our 130 ppm odor threshold, we can detect its presence, long before we reach levels of concern.

Because it is a simple Alkane and relatively non toxic, hexane is used extensively in food extraction, but should not be viewed as being as salubrious as mother’s milk.

The first clue of course, is that it doesn’t come in nearly as attractive a container, and the second is the MSDS information which tells us, that in excess, N-Hexane attacks our nervous system.  The following is a typical MSDS Section 8:

Section 8: Exposure Controls/Personal Protection

Engineering Controls:

Provide exhaust ventilation or other engineering controls to keep the airborne concentrations of vapors below their respective threshold limit value. Ensure that eyewash stations and safety showers are proximal to the work-station location.

Personal Protection:

Safety glasses. Lab coat. Vapor respirator. Be sure to use an approved/certified respirator or equivalent. Gloves (impervious).

Exposure Limits:

TWA: 500 (ppm) from OSHA (PEL) [United States] Inhalation

TWA: 1800 (mg/m3) from OSHA (PEL) [United States] Inhalation TWA: 176 (mg/m3) from ACGIH (TLV) [United States] SKIN TWA: 50 (ppm) from ACGIH (TLV) [United States] SKIN TWA:

500 STEL: 1000 (ppm) from ACGIH (TLV) [United States] Inhalation TWA: 1760 STEL: 3500 (mg/m3) from ACGIH (TLV)

Section 11: Toxicological Information

Routes of Entry: Absorbed through skin. Dermal contact. Inhalation. Ingestion.

Toxicity to Animals:


Acute oral toxicity (LD50): 25000 mg/kg [Rat]. Acute toxicity of the gas (LC50): 48000 ppm 4 hours [Rat].

As the saying goes, the poison is in the dosage, so leave us please keep N-Hexane’s potential nature in perspective, which includes never losing sight of it.  Note also that oxygen in a breathing atmosphere greater than 75% pure will kill us dead!

A review of the hexane Material Safety Data Sheet shows that the oral rat LD50: is relatively high at 25000 mg/kg.

Acute toxicity of the gas (LC50 rat): was 48000 ppm using 4 hours exposure data and the Threshold Limit Value for an 8 hour weighted average in breathing air is 500 ppm with a Permitted Exposure Limit of 1800 mg/M3 (~ppm).

Studies of shoe repair folks suggest that long term chronic exposure at lower limits can have long term effects, because the liver converts n-hexane to Hexane 2.5 dione.  Their chronic exposure was many times what you would encounter in purging residuals left in oil that is below sensory threshold.

Besides NIOSH, we also have U.S. Department of Health and Human Services, Food and Drug Administration, Center for Drug Evaluation and Research (CDER), Center for Biologics Evaluation and Research (CBER) regulating what you can use and what you can leave behind:


They list n-Hexane as a class two solvent with 290 ppm concentration limits, and a total PDE of 290 mg/day.

The good news is that if you are out of the stink or taste, you are less than about .01% of TLV, but the bad news (?) is that although it is relatively non toxic, hexane still tastes like lighter fluid below toxicity levels, with our 130 ppm sensory threshold far below the Threshold Limit Value.


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